Mr. Quinn & Ms. Tom February 24, 2014 Aim: How do we determine where energy goes in a chemical reaction? Do Now: List one reaction that increases the surrounding temperature, and one reaction the decreases the surrounding temperature.

The Laws of Thermodynamics Energy cannot be created or destroyed The disorder of a system increases over time

Endothermic Reactions Two Types of Reactions Exothermic Reactions Temperature increases Energy is released Heat is a product Endothermic Reactions Temperature decreases Energy is absorbed Heat is a reactant

Example 1

Example 1 Did the temperature of the surroundings increase or decrease? INCREASE Is the reaction pictured exothermic or endothermic? EXOTHERMIC Provide one justification for your answer to the previous question. TEMPERATURE INCREASED AND THERE WAS A FIRE Where was the energy released to? THE AIR Would you predict that the products have a higher or lower energy than the reactants?

Example 2

Example 2 Did the temperature of the surroundings increase or decrease? DECREASE Is the reaction pictured exothermic or endothermic? ENDOTHERMIC Provide one justification for your answer to the previous question. TEMPERATURE DECREASCED Where was the energy absorbed from? THE WATER Would you predict that the products have a higher or lower energy than the reactants?

Let’s Try It Out! Melting ice causes the temperature of the air to DECREASE. Is the process of melting exothermic or endothermic? Why?   When water vapor forms snow (deposition), the temperature of the air INCREASES. Is deposition exothermic or endothermic? Why?

Let’s Try It Out! Dissolving table salt in water is endothermic. What do you expect to happen to the temperature of the water?   Burning Mg creates a hot white flame. Is this process exothermic or endothermic? Explain.

Let’s Try It Out! A process is exothermic. Is energy a product or reactant?    A process leaves products with less energy than the reactants. Is it exothermic or endothermic?

Your Turn!